AP PhotoSupporter of WikiLeaks founder, Julian Assange, hold posters with his photo during a protest in front of the British Embassy in Madrid, Spain.

Rafix was set to attack.
The target: Visa.com. The weapon: a battery of personal computers ready
to jam the site with millions of simultaneous log-in requests.

"FIRE AT WILL, gentlemen!" Rafix wrote in an online message. "Enjoy the EPIC battle of GLORY!"

Within
seconds of the battle cry, the attackers crippled the website of the
world's largest credit card company. Unable to weather the massive surge
in traffic, Visa's site was out of commission for most of the day.

Visa
came under fire for its decision to suspend the processing of donations
to WikiLeaks, the controversial website that has been publishing
confidential U.S. government documents. The attack was coordinated
through an Internet chat room where more than 1,000 online activists
were signed in, massing for the call to fire.

Angry about what
they saw as an infringement of Internet freedom, hacker activists also
launched successful attacks Wednesday on websites for MasterCard,
PayPal, Swiss bank Post-Finance and the Swedish prosecutor leading the
sexual assault case against WikiLeaks founder Julian Assange.

The
"hacktivists," working under the banner of Operation Payback, are part
of a new breed of online protesters who say they are ready to engage in
acts of cyber-disobedience against major corporations, politicians and
religious institutions, all in the name of defending their ideals.

But
some believe that these digital crusaders are more interested in using
their skills to do damage than they are in making a political statement.

"What
I'm seeing in my nerd brethren is an increasing combativeness, a loss
of empathy, and creepiness," said Jaron Lanier, a critic of digital
culture and a pioneering computer scientist who helped develop virtual
reality. "It's just another supremacy movement, ultimately. It just
happens to be nerd supremacy."

The membership of these groups is
fluid, and tends to consist of unidentified Internet denizens, giving
rise to the catchall name their members use: Anonymous. The code name
Rafix probably was created moments before the attack.

Their tactic
of choice is the "distributed denial of service" attack, a kind of
Internet blitz that comes when the attackers try to jam a company's
website by getting large numbers of computers to contact it at the same
time, a bit like a group of pickets blocking the entrance to a grocery
store.

In the latest incidents, the attackers made use of a
specially designed hacker weapon dubbed the "Low Orbit Ion Cannon" after
a space laser in the "Star Wars" movies. The Cannon, actually a
software program anyone could download, allowed the group's leaders to
take control of members' computers in order to aim them, en masse, at
target websites.

"Corrupt governments of the world," began a
recent message on the group's YouTube site. "To move to censor content
on the Internet based on your own prejudice is, at best, laughably
impossible, at worst, morally reprehensible."

Hacking has been
around as long as the Internet, but has generally been the province of
vandals, organized criminals or programmers simply flaunting their
technical prowess, said Marc Cooper, a professor at USC's Annenberg
School for Communication and Journalism.

"This is the first time we're really seeing a mass movement of cyber-sabotage with political overtones," he said.

"Whatever the legality and morality, I think it has an undeniable Robin Hood type of resonance with lots of people."

As
is true of WikiLeaks, the members of Anonymous come from many
countries, work in secret and often set their own rules, haranguing
adversaries by barraging websites, breaking into e-mail accounts and
posting targets' personal information on the Web.

This year, the
sites of the Recording Industry Assn. of America and the Motion Picture
Assn. of America were brought down temporarily by attackers furious
about the organizations' efforts to stop online file-sharing.

Law
enforcement authorities say these attacks, which can cause severe
disruption to businesses, can easily cross the line from demonstration
to criminal action.

On Thursday, Dutch police arrested a
16-year-old boy for participating in the attack against Visa as well as
one against MasterCard. The boy confessed to participating in the
assaults, according to a statement from the Netherlands' national
prosecutor.

Last month, 22-year-old David Kernell was sentenced to
one year in prison for breaking into the personal e-mail account of
then-vice presidential candidate Sarah Palin in 2008 and posting some of
her e-mails online. Kernell had been allied with a message board called
4Chan that is a frequent gathering place for Anonymous agitators.

And last year, a New Jersey man pleaded guilty to having launched an attack against the Church of Scientology's website in 2008.

In
an online manifesto, Anonymous members quoted Electronic Frontier
Foundation co-founder John Perry Barlow, who had sent out a tweet last
week saying, "The first serious info war is now engaged. The field of
battle is WikiLeaks. You are the troops."

Reached by phone this
week, Barlow said he was impressed by how quickly Anonymous had
organized against its foes, but said he did not condone the attacks.

"I
don't think that if you're trying to convey the right to know, the
answer is to shut somebody up," said Barlow, who is a fellow at
Harvard's Berkman Center for Internet and Society.

To be sure, the
group also encouraged people to promote Assange's cause via Facebook,
MySpace, Twitter and other means, noting that "social networking sites
are critical hubs of information distribution."

But Anonymous' Twitter and Facebook accounts were themselves suspended.

Facebook said the account owners were violating its terms of use by promoting the attacks.

Twitter
would not comment on the specifics of its decision, but the last tweet
on Anonymous' account claimed to link to credit card information from
MasterCard users. (MasterCard said the credit card numbers were bogus.)

Still,
after a day on which it took down the websites of major companies and
political figures around the world, Anonymous gave itself a virtual pat
on the back.